Adding upstream version 2.10.36.upstream/2.10.36

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1449 insertions, 0 deletions

diff --git a/app/display/gimpdisplayshell-scale.c b/app/display/gimpdisplayshell-scale.c
new file mode 100644
index 0000000..482a9fe
--- /dev/null
+++ b/app/display/gimpdisplayshell-scale.c
@@ -0,0 +1,1449 @@
+/* GIMP - The GNU Image Manipulation Program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <math.h>
+
+#include <gegl.h>
+#include <gtk/gtk.h>
+
+#include "libgimpbase/gimpbase.h"
+#include "libgimpmath/gimpmath.h"
+#include "libgimpwidgets/gimpwidgets.h"
+
+#include "display-types.h"
+
+#include "config/gimpguiconfig.h"
+
+#include "core/gimp.h"
+#include "core/gimpimage.h"
+
+#include "gimpdisplay.h"
+#include "gimpdisplayshell.h"
+#include "gimpdisplayshell-expose.h"
+#include "gimpdisplayshell-rotate.h"
+#include "gimpdisplayshell-scale.h"
+#include "gimpdisplayshell-scroll.h"
+#include "gimpdisplayshell-transform.h"
+#include "gimpimagewindow.h"
+
+
+#define SCALE_TIMEOUT             2
+#define SCALE_EPSILON             0.0001
+#define ALMOST_CENTERED_THRESHOLD 2
+
+#define SCALE_EQUALS(a,b) (fabs ((a) - (b)) < SCALE_EPSILON)
+
+
+/*  local function prototypes  */
+
+static void      gimp_display_shell_scale_get_screen_resolution
+                                                         (GimpDisplayShell *shell,
+                                                          gdouble          *xres,
+                                                          gdouble          *yres);
+static void      gimp_display_shell_scale_get_image_size_for_scale
+                                                         (GimpDisplayShell *shell,
+                                                          gdouble           scale,
+                                                          gint             *w,
+                                                          gint             *h);
+static void      gimp_display_shell_calculate_scale_x_and_y
+                                                         (GimpDisplayShell *shell,
+                                                          gdouble           scale,
+                                                          gdouble          *scale_x,
+                                                          gdouble          *scale_y);
+
+static void      gimp_display_shell_scale_to             (GimpDisplayShell *shell,
+                                                          gdouble           scale,
+                                                          gdouble           viewport_x,
+                                                          gdouble           viewport_y);
+static void      gimp_display_shell_scale_fit_or_fill    (GimpDisplayShell *shell,
+                                                          gboolean          fill);
+
+static gboolean  gimp_display_shell_scale_image_starts_to_fit
+                                                         (GimpDisplayShell *shell,
+                                                          gdouble           new_scale,
+                                                          gdouble           current_scale,
+                                                          gboolean         *vertically,
+                                                          gboolean         *horizontally);
+static gboolean  gimp_display_shell_scale_viewport_coord_almost_centered
+                                                         (GimpDisplayShell *shell,
+                                                          gint              x,
+                                                          gint              y,
+                                                          gboolean         *horizontally,
+                                                          gboolean         *vertically);
+
+static void      gimp_display_shell_scale_get_image_center_viewport
+                                                         (GimpDisplayShell *shell,
+                                                          gint             *image_center_x,
+                                                          gint             *image_center_y);
+
+
+static void      gimp_display_shell_scale_get_zoom_focus (GimpDisplayShell *shell,
+                                                          gdouble           new_scale,
+                                                          gdouble           current_scale,
+                                                          gdouble          *x,
+                                                          gdouble          *y,
+                                                          GimpZoomFocus     zoom_focus);
+
+
+/*  public functions  */
+
+/**
+ * gimp_display_shell_scale_revert:
+ * @shell:     the #GimpDisplayShell
+ *
+ * Reverts the display to the previously used scale. If no previous
+ * scale exist, then the call does nothing.
+ *
+ * Return value: %TRUE if the scale was reverted, otherwise %FALSE.
+ **/
+gboolean
+gimp_display_shell_scale_revert (GimpDisplayShell *shell)
+{
+  g_return_val_if_fail (GIMP_IS_DISPLAY_SHELL (shell), FALSE);
+
+  /* don't bother if no scale has been set */
+  if (shell->last_scale < SCALE_EPSILON)
+    return FALSE;
+
+  shell->last_scale_time = 0;
+
+  gimp_display_shell_scale_by_values (shell,
+                                      shell->last_scale,
+                                      shell->last_offset_x,
+                                      shell->last_offset_y,
+                                      FALSE);   /* don't resize the window */
+
+  return TRUE;
+}
+
+/**
+ * gimp_display_shell_scale_can_revert:
+ * @shell: the #GimpDisplayShell
+ *
+ * Return value: %TRUE if a previous display scale exists, otherwise %FALSE.
+ **/
+gboolean
+gimp_display_shell_scale_can_revert (GimpDisplayShell *shell)
+{
+  g_return_val_if_fail (GIMP_IS_DISPLAY_SHELL (shell), FALSE);
+
+  return (shell->last_scale > SCALE_EPSILON);
+}
+
+/**
+ * gimp_display_shell_scale_save_revert_values:
+ * @shell:
+ *
+ * Handle the updating of the Revert Zoom variables.
+ **/
+void
+gimp_display_shell_scale_save_revert_values (GimpDisplayShell *shell)
+{
+  guint now;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  now = time (NULL);
+
+  if (now - shell->last_scale_time >= SCALE_TIMEOUT)
+    {
+      shell->last_scale    = gimp_zoom_model_get_factor (shell->zoom);
+      shell->last_offset_x = shell->offset_x;
+      shell->last_offset_y = shell->offset_y;
+    }
+
+  shell->last_scale_time = now;
+}
+
+/**
+ * gimp_display_shell_scale_set_dot_for_dot:
+ * @shell:        the #GimpDisplayShell
+ * @dot_for_dot:  whether "Dot for Dot" should be enabled
+ *
+ * If @dot_for_dot is set to %TRUE then the "Dot for Dot" mode (where image and
+ * screen pixels are of the same size) is activated. Dually, the mode is
+ * disabled if @dot_for_dot is %FALSE.
+ **/
+void
+gimp_display_shell_scale_set_dot_for_dot (GimpDisplayShell *shell,
+                                          gboolean          dot_for_dot)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  if (dot_for_dot != shell->dot_for_dot)
+    {
+      GimpDisplayConfig *config = shell->display->config;
+      gboolean           resize_window;
+
+      /* Resize windows only in multi-window mode */
+      resize_window = (config->resize_windows_on_zoom &&
+                       ! GIMP_GUI_CONFIG (config)->single_window_mode);
+
+      /* freeze the active tool */
+      gimp_display_shell_pause (shell);
+
+      shell->dot_for_dot = dot_for_dot;
+
+      gimp_display_shell_scale_update (shell);
+
+      gimp_display_shell_scale_resize (shell, resize_window, FALSE);
+
+      /* re-enable the active tool */
+      gimp_display_shell_resume (shell);
+    }
+}
+
+/**
+ * gimp_display_shell_scale_get_image_size:
+ * @shell:
+ * @w:
+ * @h:
+ *
+ * Gets the size of the rendered image after it has been scaled.
+ *
+ **/
+void
+gimp_display_shell_scale_get_image_size (GimpDisplayShell *shell,
+                                         gint             *w,
+                                         gint             *h)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  gimp_display_shell_scale_get_image_size_for_scale (shell,
+                                                     gimp_zoom_model_get_factor (shell->zoom),
+                                                     w, h);
+}
+
+/**
+ * gimp_display_shell_scale_get_image_bounds:
+ * @shell:
+ * @x:
+ * @y:
+ * @w:
+ * @h:
+ *
+ * Gets the screen-space boudning box of the image, after it has
+ * been transformed (i.e., scaled, rotated, and scrolled).
+ **/
+void
+gimp_display_shell_scale_get_image_bounds (GimpDisplayShell *shell,
+                                           gint             *x,
+                                           gint             *y,
+                                           gint             *w,
+                                           gint             *h)
+{
+  GimpImage *image;
+  gdouble    x1, y1;
+  gdouble    x2, y2;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  image = gimp_display_get_image (shell->display);
+
+  gimp_display_shell_transform_bounds (shell,
+                                       0, 0,
+                                       gimp_image_get_width (image),
+                                       gimp_image_get_height (image),
+                                       &x1, &y1,
+                                       &x2, &y2);
+
+  x1 = ceil (x1);
+  y1 = ceil (y1);
+  x2 = floor (x2);
+  y2 = floor (y2);
+
+  if (x) *x = x1 + shell->offset_x;
+  if (y) *y = y1 + shell->offset_y;
+  if (w) *w = x2 - x1;
+  if (h) *h = y2 - y1;
+}
+
+/**
+ * gimp_display_shell_scale_get_image_unrotated_bounds:
+ * @shell:
+ * @x:
+ * @y:
+ * @w:
+ * @h:
+ *
+ * Gets the screen-space boudning box of the image, after it has
+ * been scaled and scrolled, but before it has been rotated.
+ **/
+void
+gimp_display_shell_scale_get_image_unrotated_bounds (GimpDisplayShell *shell,
+                                                     gint             *x,
+                                                     gint             *y,
+                                                     gint             *w,
+                                                     gint             *h)
+{
+  GimpImage *image;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  image = gimp_display_get_image (shell->display);
+
+  if (x) *x = -shell->offset_x;
+  if (y) *y = -shell->offset_y;
+  if (w) *w = floor (gimp_image_get_width  (image) * shell->scale_x);
+  if (h) *h = floor (gimp_image_get_height (image) * shell->scale_y);
+}
+
+/**
+ * gimp_display_shell_scale_get_image_bounding_box:
+ * @shell:
+ * @x:
+ * @y:
+ * @w:
+ * @h:
+ *
+ * Gets the screen-space boudning box of the image content, after it has
+ * been transformed (i.e., scaled, rotated, and scrolled).
+ **/
+void
+gimp_display_shell_scale_get_image_bounding_box (GimpDisplayShell *shell,
+                                                 gint             *x,
+                                                 gint             *y,
+                                                 gint             *w,
+                                                 gint             *h)
+{
+  GeglRectangle bounding_box;
+  gdouble       x1, y1;
+  gdouble       x2, y2;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  bounding_box = gimp_display_shell_get_bounding_box (shell);
+
+  gimp_display_shell_transform_bounds (shell,
+                                       bounding_box.x,
+                                       bounding_box.y,
+                                       bounding_box.x + bounding_box.width,
+                                       bounding_box.y + bounding_box.height,
+                                       &x1, &y1,
+                                       &x2, &y2);
+
+  if (! shell->show_all)
+    {
+      x1 = ceil  (x1);
+      y1 = ceil  (y1);
+      x2 = floor (x2);
+      y2 = floor (y2);
+    }
+  else
+    {
+      x1 = floor (x1);
+      y1 = floor (y1);
+      x2 = ceil  (x2);
+      y2 = ceil  (y2);
+    }
+
+  if (x) *x = x1 + shell->offset_x;
+  if (y) *y = y1 + shell->offset_y;
+  if (w) *w = x2 - x1;
+  if (h) *h = y2 - y1;
+}
+
+/**
+ * gimp_display_shell_scale_get_image_unrotated_bounding_box:
+ * @shell:
+ * @x:
+ * @y:
+ * @w:
+ * @h:
+ *
+ * Gets the screen-space boudning box of the image content, after it has
+ * been scaled and scrolled, but before it has been rotated.
+ **/
+void
+gimp_display_shell_scale_get_image_unrotated_bounding_box (GimpDisplayShell *shell,
+                                                           gint             *x,
+                                                           gint             *y,
+                                                           gint             *w,
+                                                           gint             *h)
+{
+  GeglRectangle bounding_box;
+  gdouble       x1, y1;
+  gdouble       x2, y2;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  bounding_box = gimp_display_shell_get_bounding_box (shell);
+
+  x1 = bounding_box.x * shell->scale_x -
+       shell->offset_x;
+  y1 = bounding_box.y * shell->scale_y -
+       shell->offset_y;
+
+  x2 = (bounding_box.x + bounding_box.width)  * shell->scale_x -
+       shell->offset_x;
+  y2 = (bounding_box.y + bounding_box.height) * shell->scale_y -
+       shell->offset_y;
+
+  if (! shell->show_all)
+    {
+      x1 = ceil  (x1);
+      y1 = ceil  (y1);
+      x2 = floor (x2);
+      y2 = floor (y2);
+    }
+  else
+    {
+      x1 = floor (x1);
+      y1 = floor (y1);
+      x2 = ceil  (x2);
+      y2 = ceil  (y2);
+    }
+
+  if (x) *x = x1;
+  if (y) *y = y1;
+  if (w) *w = x2 - x1;
+  if (h) *h = y2 - y1;
+}
+
+/**
+ * gimp_display_shell_scale_image_is_within_viewport:
+ * @shell:
+ *
+ * Returns: %TRUE if the (scaled) image is smaller than and within the
+ *          viewport.
+ **/
+gboolean
+gimp_display_shell_scale_image_is_within_viewport (GimpDisplayShell *shell,
+                                                   gboolean         *horizontally,
+                                                   gboolean         *vertically)
+{
+  gboolean horizontally_dummy, vertically_dummy;
+
+  g_return_val_if_fail (GIMP_IS_DISPLAY_SHELL (shell), FALSE);
+
+  if (! horizontally) horizontally = &horizontally_dummy;
+  if (! vertically)   vertically   = &vertically_dummy;
+
+  if (! gimp_display_shell_get_infinite_canvas (shell))
+    {
+      gint sx, sy;
+      gint sw, sh;
+
+      gimp_display_shell_scale_get_image_bounding_box (shell,
+                                                       &sx, &sy, &sw, &sh);
+
+      sx -= shell->offset_x;
+      sy -= shell->offset_y;
+
+      *horizontally = sx >= 0 && sx + sw <= shell->disp_width;
+      *vertically   = sy >= 0 && sy + sh <= shell->disp_height;
+    }
+  else
+    {
+      *horizontally = FALSE;
+      *vertically   = FALSE;
+    }
+
+  return *vertically && *horizontally;
+}
+
+/* We used to calculate the scale factor in the SCALEFACTOR_X() and
+ * SCALEFACTOR_Y() macros. But since these are rather frequently
+ * called and the values rarely change, we now store them in the
+ * shell and call this function whenever they need to be recalculated.
+ */
+void
+gimp_display_shell_scale_update (GimpDisplayShell *shell)
+{
+  GimpImage *image;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  image = gimp_display_get_image (shell->display);
+
+  if (image)
+    {
+      gimp_display_shell_calculate_scale_x_and_y (shell,
+                                                  gimp_zoom_model_get_factor (shell->zoom),
+                                                  &shell->scale_x,
+                                                  &shell->scale_y);
+    }
+  else
+    {
+      shell->scale_x = 1.0;
+      shell->scale_y = 1.0;
+    }
+}
+
+/**
+ * gimp_display_shell_scale:
+ * @shell:     the #GimpDisplayShell
+ * @zoom_type: whether to zoom in, out or to a specific scale
+ * @scale:     ignored unless @zoom_type == %GIMP_ZOOM_TO
+ *
+ * This function figures out the context of the zoom and behaves
+ * appropriately thereafter.
+ *
+ **/
+void
+gimp_display_shell_scale (GimpDisplayShell *shell,
+                          GimpZoomType      zoom_type,
+                          gdouble           new_scale,
+                          GimpZoomFocus     zoom_focus)
+{
+  GimpDisplayConfig *config;
+  gdouble            current_scale;
+  gboolean           resize_window;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+  g_return_if_fail (shell->canvas != NULL);
+
+  current_scale = gimp_zoom_model_get_factor (shell->zoom);
+
+  if (zoom_type != GIMP_ZOOM_TO)
+    new_scale = gimp_zoom_model_zoom_step (zoom_type, current_scale);
+
+  if (SCALE_EQUALS (new_scale, current_scale))
+    return;
+
+  config = shell->display->config;
+
+  /* Resize windows only in multi-window mode */
+  resize_window = (config->resize_windows_on_zoom &&
+                   ! GIMP_GUI_CONFIG (config)->single_window_mode);
+
+  if (resize_window)
+    {
+      /* If the window is resized on zoom, simply do the zoom and get
+       * things rolling
+       */
+      gimp_zoom_model_zoom (shell->zoom, GIMP_ZOOM_TO, new_scale);
+
+      gimp_display_shell_scale_resize (shell, TRUE, FALSE);
+    }
+  else
+    {
+      gdouble  x, y;
+      gint     image_center_x;
+      gint     image_center_y;
+
+      gimp_display_shell_scale_get_zoom_focus (shell,
+                                               new_scale,
+                                               current_scale,
+                                               &x,
+                                               &y,
+                                               zoom_focus);
+      gimp_display_shell_scale_get_image_center_viewport (shell,
+                                                          &image_center_x,
+                                                          &image_center_y);
+
+      gimp_display_shell_scale_to (shell, new_scale, x, y);
+
+      /* skip centering magic if pointer focus was requested */
+      if (zoom_focus != GIMP_ZOOM_FOCUS_POINTER)
+        {
+          gboolean starts_fitting_horiz;
+          gboolean starts_fitting_vert;
+          gboolean zoom_focus_almost_centered_horiz;
+          gboolean zoom_focus_almost_centered_vert;
+          gboolean image_center_almost_centered_horiz;
+          gboolean image_center_almost_centered_vert;
+
+          /* If an image axis started to fit due to zooming out or if
+           * the focus point is as good as in the center, center on
+           * that axis
+           */
+          gimp_display_shell_scale_image_starts_to_fit (shell,
+                                                        new_scale,
+                                                        current_scale,
+                                                        &starts_fitting_horiz,
+                                                        &starts_fitting_vert);
+
+          gimp_display_shell_scale_viewport_coord_almost_centered (shell,
+                                                                   x,
+                                                                   y,
+                                                                   &zoom_focus_almost_centered_horiz,
+                                                                   &zoom_focus_almost_centered_vert);
+          gimp_display_shell_scale_viewport_coord_almost_centered (shell,
+                                                                   image_center_x,
+                                                                   image_center_y,
+                                                                   &image_center_almost_centered_horiz,
+                                                                   &image_center_almost_centered_vert);
+
+          gimp_display_shell_scroll_center_image (shell,
+                                                  starts_fitting_horiz ||
+                                                  (zoom_focus_almost_centered_horiz &&
+                                                   image_center_almost_centered_horiz),
+                                                  starts_fitting_vert ||
+                                                  (zoom_focus_almost_centered_vert &&
+                                                   image_center_almost_centered_vert));
+        }
+    }
+}
+
+/**
+ * gimp_display_shell_scale_to_rectangle:
+ * @shell:         the #GimpDisplayShell
+ * @zoom_type:     whether to zoom in or out
+ * @x:             retangle's x in image coordinates
+ * @y:             retangle's y in image coordinates
+ * @width:         retangle's width in image coordinates
+ * @height:        retangle's height in image coordinates
+ * @resize_window: whether the display window should be resized
+ *
+ * Scales and scrolls to a specific image rectangle
+ **/
+void
+gimp_display_shell_scale_to_rectangle (GimpDisplayShell *shell,
+                                       GimpZoomType      zoom_type,
+                                       gdouble           x,
+                                       gdouble           y,
+                                       gdouble           width,
+                                       gdouble           height,
+                                       gboolean          resize_window)
+{
+  gdouble current_scale;
+  gdouble new_scale;
+  gdouble factor   = 1.0;
+  gint    offset_x = 0;
+  gint    offset_y = 0;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  gimp_display_shell_transform_bounds (shell,
+                                       x, y,
+                                       x + width, y + height,
+                                       &x, &y,
+                                       &width, &height);
+
+  /* Convert scrolled (x1, y1, x2, y2) to unscrolled (x, y, width, height). */
+  width  -= x;
+  height -= y;
+  x      += shell->offset_x;
+  y      += shell->offset_y;
+
+  width  = MAX (1.0, width);
+  height = MAX (1.0, height);
+
+  current_scale = gimp_zoom_model_get_factor (shell->zoom);
+
+  switch (zoom_type)
+    {
+    case GIMP_ZOOM_IN:
+      factor = MIN ((shell->disp_width  / width),
+                    (shell->disp_height / height));
+      break;
+
+    case GIMP_ZOOM_OUT:
+      factor = MAX ((width  / shell->disp_width),
+                    (height / shell->disp_height));
+      break;
+
+    default:
+      g_return_if_reached ();
+      break;
+    }
+
+  new_scale = current_scale * factor;
+
+  switch (zoom_type)
+    {
+    case GIMP_ZOOM_IN:
+      /*  move the center of the rectangle to the center of the
+       *  viewport:
+       *
+       *  new_offset = center of rectangle in new scale screen coords
+       *               including offset
+       *               -
+       *               center of viewport in screen coords without
+       *               offset
+       */
+      offset_x = RINT (factor * (x + width  / 2.0) - (shell->disp_width  / 2));
+      offset_y = RINT (factor * (y + height / 2.0) - (shell->disp_height / 2));
+      break;
+
+    case GIMP_ZOOM_OUT:
+      /*  move the center of the viewport to the center of the
+       *  rectangle:
+       *
+       *  new_offset = center of viewport in new scale screen coords
+       *               including offset
+       *               -
+       *               center of rectangle in screen coords without
+       *               offset
+       */
+      offset_x = RINT (factor * (shell->offset_x + shell->disp_width  / 2) -
+                       ((x + width  / 2.0) - shell->offset_x));
+
+      offset_y = RINT (factor * (shell->offset_y + shell->disp_height / 2) -
+                       ((y + height / 2.0) - shell->offset_y));
+      break;
+
+    default:
+      break;
+    }
+
+  if (new_scale != current_scale   ||
+      offset_x  != shell->offset_x ||
+      offset_y  != shell->offset_y)
+    {
+      gimp_display_shell_scale_by_values (shell,
+                                          new_scale,
+                                          offset_x, offset_y,
+                                          resize_window);
+    }
+}
+
+/**
+ * gimp_display_shell_scale_fit_in:
+ * @shell: the #GimpDisplayShell
+ *
+ * Sets the scale such that the entire image precisely fits in the
+ * display area.
+ **/
+void
+gimp_display_shell_scale_fit_in (GimpDisplayShell *shell)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  gimp_display_shell_scale_fit_or_fill (shell,
+                                        /* fill = */ FALSE);
+ }
+
+/**
+ * gimp_display_shell_scale_fill:
+ * @shell: the #GimpDisplayShell
+ *
+ * Sets the scale such that the entire display area is precisely
+ * filled by the image.
+ **/
+void
+gimp_display_shell_scale_fill (GimpDisplayShell *shell)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  gimp_display_shell_scale_fit_or_fill (shell,
+                                        /* fill = */ TRUE);
+}
+
+/**
+ * gimp_display_shell_scale_by_values:
+ * @shell:         the #GimpDisplayShell
+ * @scale:         the new scale
+ * @offset_x:      the new X offset
+ * @offset_y:      the new Y offset
+ * @resize_window: whether the display window should be resized
+ *
+ * Directly sets the image scale and image offsets used by the display. If
+ * @resize_window is %TRUE then the display window is resized to better
+ * accommodate the image, see gimp_display_shell_shrink_wrap().
+ **/
+void
+gimp_display_shell_scale_by_values (GimpDisplayShell *shell,
+                                    gdouble           scale,
+                                    gint              offset_x,
+                                    gint              offset_y,
+                                    gboolean          resize_window)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  /*  Abort early if the values are all setup already. We don't
+   *  want to inadvertently resize the window (bug #164281).
+   */
+  if (SCALE_EQUALS (gimp_zoom_model_get_factor (shell->zoom), scale) &&
+      shell->offset_x == offset_x &&
+      shell->offset_y == offset_y)
+    return;
+
+  gimp_display_shell_scale_save_revert_values (shell);
+
+  /* freeze the active tool */
+  gimp_display_shell_pause (shell);
+
+  gimp_zoom_model_zoom (shell->zoom, GIMP_ZOOM_TO, scale);
+
+  shell->offset_x = offset_x;
+  shell->offset_y = offset_y;
+
+  gimp_display_shell_rotate_update_transform (shell);
+
+  gimp_display_shell_scale_resize (shell, resize_window, FALSE);
+
+  /* re-enable the active tool */
+  gimp_display_shell_resume (shell);
+}
+
+void
+gimp_display_shell_scale_drag (GimpDisplayShell *shell,
+                               gdouble           start_x,
+                               gdouble           start_y,
+                               gdouble           delta_x,
+                               gdouble           delta_y)
+{
+  gdouble scale;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  scale = gimp_zoom_model_get_factor (shell->zoom);
+
+  gimp_display_shell_push_zoom_focus_pointer_pos (shell, start_x, start_y);
+
+  if (delta_y > 0)
+    {
+      gimp_display_shell_scale (shell,
+                                GIMP_ZOOM_TO,
+                                scale * 1.1,
+                                GIMP_ZOOM_FOCUS_POINTER);
+    }
+  else if (delta_y < 0)
+    {
+      gimp_display_shell_scale (shell,
+                                GIMP_ZOOM_TO,
+                                scale * 0.9,
+                                GIMP_ZOOM_FOCUS_POINTER);
+    }
+}
+
+/**
+ * gimp_display_shell_scale_shrink_wrap:
+ * @shell: the #GimpDisplayShell
+ *
+ * Convenience function with the same functionality as
+ * gimp_display_shell_scale_resize(@shell, TRUE, grow_only).
+ **/
+void
+gimp_display_shell_scale_shrink_wrap (GimpDisplayShell *shell,
+                                      gboolean          grow_only)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  gimp_display_shell_scale_resize (shell, TRUE, grow_only);
+}
+
+/**
+ * gimp_display_shell_scale_resize:
+ * @shell:          the #GimpDisplayShell
+ * @resize_window:  whether the display window should be resized
+ * @grow_only:      whether shrinking of the window is allowed or not
+ *
+ * Function commonly called after a change in display scale to make the changes
+ * visible to the user. If @resize_window is %TRUE then the display window is
+ * resized to accommodate the display image as per
+ * gimp_display_shell_shrink_wrap().
+ **/
+void
+gimp_display_shell_scale_resize (GimpDisplayShell *shell,
+                                 gboolean          resize_window,
+                                 gboolean          grow_only)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  /* freeze the active tool */
+  gimp_display_shell_pause (shell);
+
+  if (resize_window)
+    {
+      GimpImageWindow *window = gimp_display_shell_get_window (shell);
+
+      if (window && gimp_image_window_get_active_shell (window) == shell)
+        {
+          gimp_image_window_shrink_wrap (window, grow_only);
+        }
+    }
+
+  gimp_display_shell_scroll_clamp_and_update (shell);
+  gimp_display_shell_scaled (shell);
+
+  gimp_display_shell_expose_full (shell);
+
+  /* re-enable the active tool */
+  gimp_display_shell_resume (shell);
+}
+
+void
+gimp_display_shell_set_initial_scale (GimpDisplayShell *shell,
+                                      gdouble           scale,
+                                      gint             *display_width,
+                                      gint             *display_height)
+{
+  GimpImage *image;
+  GdkScreen *screen;
+  gint       image_width;
+  gint       image_height;
+  gint       shell_width;
+  gint       shell_height;
+  gint       screen_width;
+  gint       screen_height;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  image = gimp_display_get_image (shell->display);
+
+  screen = gtk_widget_get_screen (GTK_WIDGET (shell));
+
+  image_width  = gimp_image_get_width  (image);
+  image_height = gimp_image_get_height (image);
+
+  screen_width  = gdk_screen_get_width (screen)  * 0.75;
+  screen_height = gdk_screen_get_height (screen) * 0.75;
+
+  /* We need to zoom before we use SCALE[XY] */
+  gimp_zoom_model_zoom (shell->zoom, GIMP_ZOOM_TO, scale);
+
+  shell_width  = SCALEX (shell, image_width);
+  shell_height = SCALEY (shell, image_height);
+
+  if (shell->display->config->initial_zoom_to_fit)
+    {
+      /*  Limit to the size of the screen...  */
+      if (shell_width > screen_width || shell_height > screen_height)
+        {
+          gdouble new_scale;
+          gdouble current = gimp_zoom_model_get_factor (shell->zoom);
+
+          new_scale = current * MIN (((gdouble) screen_height) / shell_height,
+                                     ((gdouble) screen_width)  / shell_width);
+
+          new_scale = gimp_zoom_model_zoom_step (GIMP_ZOOM_OUT, new_scale);
+
+          /*  Since zooming out might skip a zoom step we zoom in
+           *  again and test if we are small enough.
+           */
+          gimp_zoom_model_zoom (shell->zoom, GIMP_ZOOM_TO,
+                                gimp_zoom_model_zoom_step (GIMP_ZOOM_IN,
+                                                           new_scale));
+
+          if (SCALEX (shell, image_width) > screen_width ||
+              SCALEY (shell, image_height) > screen_height)
+            gimp_zoom_model_zoom (shell->zoom, GIMP_ZOOM_TO, new_scale);
+
+          shell_width  = SCALEX (shell, image_width);
+          shell_height = SCALEY (shell, image_height);
+        }
+    }
+  else
+    {
+      /*  Set up size like above, but do not zoom to fit. Useful when
+       *  working on large images.
+       */
+      if (shell_width > screen_width)
+        shell_width = screen_width;
+
+      if (shell_height > screen_height)
+        shell_height = screen_height;
+    }
+
+  if (display_width)
+    *display_width = shell_width;
+
+  if (display_height)
+    *display_height = shell_height;
+}
+
+/**
+ * gimp_display_shell_get_rotated_scale:
+ * @shell:   the #GimpDisplayShell
+ * @scale_x: horizontal scale output
+ * @scale_y: vertical scale output
+ *
+ * Returns the screen space horizontal and vertical scaling
+ * factors, taking rotation into account.
+ **/
+void
+gimp_display_shell_get_rotated_scale (GimpDisplayShell *shell,
+                                      gdouble          *scale_x,
+                                      gdouble          *scale_y)
+{
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  if (shell->rotate_angle == 0.0 || shell->scale_x == shell->scale_y)
+    {
+      if (scale_x) *scale_x = shell->scale_x;
+      if (scale_y) *scale_y = shell->scale_y;
+    }
+  else
+    {
+      gdouble a     = G_PI * shell->rotate_angle / 180.0;
+      gdouble cos_a = cos (a);
+      gdouble sin_a = sin (a);
+
+      if (scale_x) *scale_x = 1.0 / sqrt (SQR (cos_a / shell->scale_x) +
+                                          SQR (sin_a / shell->scale_y));
+
+      if (scale_y) *scale_y = 1.0 / sqrt (SQR (cos_a / shell->scale_y) +
+                                          SQR (sin_a / shell->scale_x));
+    }
+}
+
+/**
+ * gimp_display_shell_push_zoom_focus_pointer_pos:
+ * @shell:
+ * @x:
+ * @y:
+ *
+ * When the zoom focus mechanism asks for the pointer the next time,
+ * use @x and @y.
+ **/
+void
+gimp_display_shell_push_zoom_focus_pointer_pos (GimpDisplayShell *shell,
+                                                gint              x,
+                                                gint              y)
+{
+  GdkPoint *point = g_slice_new (GdkPoint);
+  point->x = x;
+  point->y = y;
+
+  g_queue_push_head (shell->zoom_focus_pointer_queue,
+                     point);
+}
+
+
+/*  private functions   */
+
+static void
+gimp_display_shell_scale_get_screen_resolution (GimpDisplayShell *shell,
+                                                gdouble          *xres,
+                                                gdouble          *yres)
+{
+  gdouble x, y;
+
+  if (shell->dot_for_dot)
+    {
+      gimp_image_get_resolution (gimp_display_get_image (shell->display),
+                                 &x, &y);
+    }
+  else
+    {
+      x = shell->monitor_xres;
+      y = shell->monitor_yres;
+    }
+
+  if (xres) *xres = x;
+  if (yres) *yres = y;
+}
+
+/**
+ * gimp_display_shell_scale_get_image_size_for_scale:
+ * @shell:
+ * @scale:
+ * @w:
+ * @h:
+ *
+ **/
+static void
+gimp_display_shell_scale_get_image_size_for_scale (GimpDisplayShell *shell,
+                                                   gdouble           scale,
+                                                   gint             *w,
+                                                   gint             *h)
+{
+  GimpImage *image = gimp_display_get_image (shell->display);
+  gdouble    scale_x;
+  gdouble    scale_y;
+
+  gimp_display_shell_calculate_scale_x_and_y (shell, scale, &scale_x, &scale_y);
+
+  if (w) *w = scale_x * gimp_image_get_width  (image);
+  if (h) *h = scale_y * gimp_image_get_height (image);
+}
+
+/**
+ * gimp_display_shell_calculate_scale_x_and_y:
+ * @shell:
+ * @scale:
+ * @scale_x:
+ * @scale_y:
+ *
+ **/
+static void
+gimp_display_shell_calculate_scale_x_and_y (GimpDisplayShell *shell,
+                                            gdouble           scale,
+                                            gdouble          *scale_x,
+                                            gdouble          *scale_y)
+{
+  GimpImage *image = gimp_display_get_image (shell->display);
+  gdouble    xres;
+  gdouble    yres;
+  gdouble    screen_xres;
+  gdouble    screen_yres;
+
+  gimp_image_get_resolution (image, &xres, &yres);
+  gimp_display_shell_scale_get_screen_resolution (shell,
+                                                  &screen_xres, &screen_yres);
+
+  if (scale_x) *scale_x = scale * screen_xres / xres;
+  if (scale_y) *scale_y = scale * screen_yres / yres;
+}
+
+/**
+ * gimp_display_shell_scale_to:
+ * @shell:
+ * @scale:
+ * @viewport_x:
+ * @viewport_y:
+ *
+ * Zooms. The display offsets are adjusted so that the point specified
+ * by @x and @y doesn't change it's position on screen.
+ **/
+static void
+gimp_display_shell_scale_to (GimpDisplayShell *shell,
+                             gdouble           scale,
+                             gdouble           viewport_x,
+                             gdouble           viewport_y)
+{
+  gdouble image_x, image_y;
+  gdouble new_viewport_x, new_viewport_y;
+
+  g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
+
+  if (! shell->display)
+    return;
+
+  /* freeze the active tool */
+  gimp_display_shell_pause (shell);
+
+  gimp_display_shell_untransform_xy_f (shell,
+                                       viewport_x,
+                                       viewport_y,
+                                       &image_x,
+                                       &image_y);
+
+  /* Note that we never come here if we need to resize_windows_on_zoom
+   */
+  gimp_display_shell_scale_by_values (shell,
+                                      scale,
+                                      shell->offset_x,
+                                      shell->offset_y,
+                                      FALSE);
+
+  gimp_display_shell_transform_xy_f (shell,
+                                     image_x,
+                                     image_y,
+                                     &new_viewport_x,
+                                     &new_viewport_y);
+
+  gimp_display_shell_scroll (shell,
+                             new_viewport_x - viewport_x,
+                             new_viewport_y - viewport_y);
+
+  /* re-enable the active tool */
+  gimp_display_shell_resume (shell);
+}
+
+/**
+ * gimp_display_shell_scale_fit_or_fill:
+ * @shell: the #GimpDisplayShell
+ * @fill:  whether to scale the image to fill the viewport,
+ *         or fit inside the viewport
+ *
+ * A common implementation for gimp_display_shell_scale_{fit_in,fill}().
+ **/
+static void
+gimp_display_shell_scale_fit_or_fill (GimpDisplayShell *shell,
+                                      gboolean          fill)
+{
+  GeglRectangle bounding_box;
+  gdouble       image_x;
+  gdouble       image_y;
+  gdouble       image_width;
+  gdouble       image_height;
+  gdouble       current_scale;
+  gdouble       zoom_factor;
+
+  if (! gimp_display_shell_get_infinite_canvas (shell))
+    {
+      GimpImage *image = gimp_display_get_image (shell->display);
+
+      bounding_box.x      = 0;
+      bounding_box.y      = 0;
+      bounding_box.width  = gimp_image_get_width  (image);
+      bounding_box.height = gimp_image_get_height (image);
+    }
+  else
+    {
+      bounding_box = gimp_display_shell_get_bounding_box (shell);
+    }
+
+  gimp_display_shell_transform_bounds (shell,
+                                       bounding_box.x,
+                                       bounding_box.y,
+                                       bounding_box.x + bounding_box.width,
+                                       bounding_box.y + bounding_box.height,
+                                       &image_x,
+                                       &image_y,
+                                       &image_width,
+                                       &image_height);
+
+  image_width  -= image_x;
+  image_height -= image_y;
+
+  current_scale = gimp_zoom_model_get_factor (shell->zoom);
+
+  if (fill)
+    {
+      zoom_factor = MAX (shell->disp_width  / image_width,
+                         shell->disp_height / image_height);
+    }
+  else
+    {
+      zoom_factor = MIN (shell->disp_width  / image_width,
+                         shell->disp_height / image_height);
+    }
+
+  gimp_display_shell_scale (shell,
+                            GIMP_ZOOM_TO,
+                            zoom_factor * current_scale,
+                            GIMP_ZOOM_FOCUS_BEST_GUESS);
+
+  gimp_display_shell_scroll_center_content (shell, TRUE, TRUE);
+}
+
+static gboolean
+gimp_display_shell_scale_image_starts_to_fit (GimpDisplayShell *shell,
+                                              gdouble           new_scale,
+                                              gdouble           current_scale,
+                                              gboolean         *vertically,
+                                              gboolean         *horizontally)
+{
+  gboolean vertically_dummy;
+  gboolean horizontally_dummy;
+
+  if (! vertically)   vertically   = &vertically_dummy;
+  if (! horizontally) horizontally = &horizontally_dummy;
+
+  /* The image can only start to fit if we zoom out */
+  if (new_scale > current_scale ||
+      gimp_display_shell_get_infinite_canvas (shell))
+    {
+      *vertically   = FALSE;
+      *horizontally = FALSE;
+    }
+  else
+    {
+      gint current_scale_width;
+      gint current_scale_height;
+      gint new_scale_width;
+      gint new_scale_height;
+
+      gimp_display_shell_scale_get_image_size_for_scale (shell,
+                                                         current_scale,
+                                                         &current_scale_width,
+                                                         &current_scale_height);
+
+      gimp_display_shell_scale_get_image_size_for_scale (shell,
+                                                         new_scale,
+                                                         &new_scale_width,
+                                                         &new_scale_height);
+
+      *vertically   = (current_scale_width  >  shell->disp_width &&
+                       new_scale_width      <= shell->disp_width);
+      *horizontally = (current_scale_height >  shell->disp_height &&
+                       new_scale_height     <= shell->disp_height);
+    }
+
+  return *vertically && *horizontally;
+}
+
+static gboolean
+gimp_display_shell_scale_image_stops_to_fit (GimpDisplayShell *shell,
+                                             gdouble           new_scale,
+                                             gdouble           current_scale,
+                                             gboolean         *vertically,
+                                             gboolean         *horizontally)
+{
+  return gimp_display_shell_scale_image_starts_to_fit (shell,
+                                                       current_scale,
+                                                       new_scale,
+                                                       vertically,
+                                                       horizontally);
+}
+
+/**
+ * gimp_display_shell_scale_viewport_coord_almost_centered:
+ * @shell:
+ * @x:
+ * @y:
+ * @horizontally:
+ * @vertically:
+ *
+ **/
+static gboolean
+gimp_display_shell_scale_viewport_coord_almost_centered (GimpDisplayShell *shell,
+                                                         gint              x,
+                                                         gint              y,
+                                                         gboolean         *horizontally,
+                                                         gboolean         *vertically)
+{
+  gboolean local_horizontally = FALSE;
+  gboolean local_vertically   = FALSE;
+  gint     center_x           = shell->disp_width  / 2;
+  gint     center_y           = shell->disp_height / 2;
+
+  if (! gimp_display_shell_get_infinite_canvas (shell))
+    {
+      local_horizontally = (x > center_x - ALMOST_CENTERED_THRESHOLD &&
+                            x < center_x + ALMOST_CENTERED_THRESHOLD);
+
+      local_vertically   = (y > center_y - ALMOST_CENTERED_THRESHOLD &&
+                            y < center_y + ALMOST_CENTERED_THRESHOLD);
+    }
+
+  if (horizontally) *horizontally = local_horizontally;
+  if (vertically)   *vertically   = local_vertically;
+
+  return local_horizontally && local_vertically;
+}
+
+static void
+gimp_display_shell_scale_get_image_center_viewport (GimpDisplayShell *shell,
+                                                    gint             *image_center_x,
+                                                    gint             *image_center_y)
+{
+  gint sw, sh;
+
+  gimp_display_shell_scale_get_image_size (shell, &sw, &sh);
+
+  if (image_center_x) *image_center_x = -shell->offset_x + sw / 2;
+  if (image_center_y) *image_center_y = -shell->offset_y + sh / 2;
+}
+
+/**
+ * gimp_display_shell_scale_get_zoom_focus:
+ * @shell:
+ * @new_scale:
+ * @x:
+ * @y:
+ *
+ * Calculates the viewport coordinate to focus on when zooming
+ * independently for each axis.
+ **/
+static void
+gimp_display_shell_scale_get_zoom_focus (GimpDisplayShell *shell,
+                                         gdouble           new_scale,
+                                         gdouble           current_scale,
+                                         gdouble          *x,
+                                         gdouble          *y,
+                                         GimpZoomFocus     zoom_focus)
+{
+  GtkWidget *window = GTK_WIDGET (gimp_display_shell_get_window (shell));
+  GdkEvent  *event;
+  gint       image_center_x;
+  gint       image_center_y;
+  gint       other_x;
+  gint       other_y;
+
+  /* Calculate stops-to-fit focus point */
+  gimp_display_shell_scale_get_image_center_viewport (shell,
+                                                      &image_center_x,
+                                                      &image_center_y);
+
+  /* Calculate other focus point, default is the canvas center */
+  other_x = shell->disp_width  / 2;
+  other_y = shell->disp_height / 2;
+
+  /*  Center on the mouse position instead of the display center if
+   *  one of the following conditions are fulfilled and pointer is
+   *  within the canvas:
+   *
+   *   (1) there's no current event (the action was triggered by an
+   *       input controller)
+   *   (2) the event originates from the canvas (a scroll event)
+   *   (3) the event originates from the window (a key press event)
+   *
+   *  Basically the only situation where we don't want to center on
+   *  mouse position is if the action is being called from a menu.
+   */
+  event = gtk_get_current_event ();
+
+  if (! event ||
+      gtk_get_event_widget (event) == shell->canvas ||
+      gtk_get_event_widget (event) == window)
+    {
+      GdkPoint *point = g_queue_pop_head (shell->zoom_focus_pointer_queue);
+      gint      canvas_pointer_x;
+      gint      canvas_pointer_y;
+
+      if (point)
+        {
+          canvas_pointer_x = point->x;
+          canvas_pointer_y = point->y;
+
+          g_slice_free (GdkPoint, point);
+        }
+      else
+        {
+          gtk_widget_get_pointer (shell->canvas,
+                                  &canvas_pointer_x,
+                                  &canvas_pointer_y);
+        }
+
+      if (canvas_pointer_x >= 0 &&
+          canvas_pointer_y >= 0 &&
+          canvas_pointer_x <  shell->disp_width &&
+          canvas_pointer_y <  shell->disp_height)
+        {
+          other_x = canvas_pointer_x;
+          other_y = canvas_pointer_y;
+        }
+    }
+
+  if (zoom_focus == GIMP_ZOOM_FOCUS_RETAIN_CENTERING_ELSE_BEST_GUESS)
+    {
+      if (gimp_display_shell_scale_viewport_coord_almost_centered (shell,
+                                                                   image_center_x,
+                                                                   image_center_y,
+                                                                   NULL,
+                                                                   NULL))
+        {
+          zoom_focus = GIMP_ZOOM_FOCUS_IMAGE_CENTER;
+        }
+      else
+        {
+          zoom_focus = GIMP_ZOOM_FOCUS_BEST_GUESS;
+        }
+    }
+
+  switch (zoom_focus)
+    {
+    case GIMP_ZOOM_FOCUS_POINTER:
+      *x = other_x;
+      *y = other_y;
+      break;
+
+    case GIMP_ZOOM_FOCUS_IMAGE_CENTER:
+      *x = image_center_x;
+      *y = image_center_y;
+      break;
+
+    case GIMP_ZOOM_FOCUS_BEST_GUESS:
+    default:
+      {
+        gboolean within_horizontally, within_vertically;
+        gboolean stops_horizontally, stops_vertically;
+
+        gimp_display_shell_scale_image_is_within_viewport (shell,
+                                                           &within_horizontally,
+                                                           &within_vertically);
+
+        gimp_display_shell_scale_image_stops_to_fit (shell,
+                                                     new_scale,
+                                                     current_scale,
+                                                     &stops_horizontally,
+                                                     &stops_vertically);
+
+        *x = within_horizontally && ! stops_horizontally ? image_center_x : other_x;
+        *y = within_vertically   && ! stops_vertically   ? image_center_y : other_y;
+      }
+      break;
+    }
+}